1. Field of the Invention
The present invention relates to a head support device, which supports a head and moves the head to a target position above a data-bearing surface of a disk for positioning. The invention also relates to a disk drive with a floating head, such as a magnetic disk drive, an optical disk drive or a magneto-optical disk drive, which uses the head support device and finds use as a recording/reproducing apparatus in a computer or the like.
2. Background Art
A disk recording/reproducing apparatus (hereinafter referred to as “disk drive”) such as a hard disk drive (HDD) uses a head to record and reproduce data on and from a data-bearing surface of a disk, which is a recording medium. The HDD is provided with a head support device, whereby the head is supported in floating condition at a specified distance from the data-bearing surface of the disk and moves radially above the disk. Including this structure, many structures have been proposed (refer to, for example, Japanese Patent Unexamined Publication No. 09-082052).
With reference to FIGS. 7 and 8, a head support device of a magnetic recording/reproducing apparatus such as the HDD is described hereinafter as an example of the head support device of the conventional disk drive with the floating head. FIG. 7 is a plan view of an essential part of the magnetic recording/reproducing apparatus, and FIG. 8 is a perspective view of the head support device.
In FIG. 7, head support device 81 is constructed of support arm 82 having relatively low rigidity, plate spring 83, base arm 84 having relatively high rigidity, slider 85 provided at one end of support arm 82 to face the disk, and a magnetic head (not shown) mounted to slider 85. Plate spring 83 is formed by folding the other end of support arm 82 and is connected to base arm 84. Base arm 84 is rotatably supported at rotary bearing 86. With driving means 87 mounted to base arm 84, head support device 81 can swing to a specified angle in a direction parallel to disk (also referred to as “magnetic recording medium” or simply “recording medium”) 88. Head support device 81, rotary bearing 86 and driving means 87 form head driving device 80.
Disk 88 is rotated at a specified speed by rotation driving means 89. When the magnetic recording/reproducing apparatus records and reproduces, slider 85 floats by a given amount of flotation as a result of a balance between flotation, which is effected by an airflow caused by the rotation of disk 88, and force urging slider 85 toward disk 88. The head performs recording and reproduction while floating by the given amount. The force urging slider 85 toward disk 88 is applied mainly by plate spring 83 of head support device 81.
In other words, in recording and reproduction, head support device 81 is caused by driving means 87 provided at base arm 84 to swing on rotary bearing 86, and while floating by the given amount over disk 88, the head mounted to slider 85 is located above a specified track to perform recording and reproduction.
Referring to FIG. 8, a further description of the structure of head support device 81 and a description of the action of support device 81 are provided next. FIG. 8 is the perspective view of head support device 81 of FIG. 7 that is provided with the magnetic head.
In FIG. 8, slider 85 provided at the end of support arm 82 to face downward is provided with the magnetic head (not shown) at its surface facing the magnetic recording medium (not shown). Plate spring 83 is formed to have flexibility. Specifically, to reduce variations in load of slider 85 with respect to magnetic recording medium 88 that result from, for example, vertical movement (e.g., a wobble) of recording medium 88 or variations in the distance between slider 85 and recording medium 88 in mass production, plate spring 83 is provided with cutout hole 90, thus having reduced rigidity and a smaller spring constant.
In such a head support device, even when the disk moves vertically in recording and reproduction on and from the disk, the slider is caused to float stably, thus preventing off-tracking or deviation of the head from the specified track of the disk. Moreover, the force, which urges the specified load of the slider toward the disk, is applied mainly by the plate spring to allow the head to well follow the vertical movement of the disk. In this way, the support arm is formed to have the flexibility. Accordingly, the plate spring is required to secure, without fail, the force necessary for urging the slider toward the disk. It is also necessary that this urging force (also referred to as “thrust force”) be prevented from varying as a result of variations in the amount of flotation of the slider in production. Providing the support arm with the cutout hole such as shown in FIG. 8 or forming the support arm into a thin plate structure reduces the rigidity as well as the spring constant, thus imparting some flexibility to the head support device for smoothing out the variations in the urging force.
It is also known that torsion of the support arm, for example, greatly affects the motion of the head support device. Japanese Patent Unexamined Publication No. 08-045214, for example, discloses a technique for reducing a torsional vibration mode or the like. According to such a technique, the curved shape of a spring section (which corresponds to the plate spring) is adjusted, and a bump (which corresponds to the magnitude of curvature of the spring section) and an offset (which corresponds to a difference in height between a junction of the support arm and the spring section and a junction of the spring section and the base arm) are optimized in order to allow the slider to remain almost motionless at a first torsional resonance frequency.
The above-mentioned head support devices including the one having the optimized bump and offset, each has the support arm formed into the thin plate structure and has a reduced frequency of a primary resonance point, that is, a reduced resonance frequency. When the head support device swings toward the specified track for positioning, a torsional vibration mode or the like occurs, and it takes time to settle this vibration mode. Consequently, it is difficult to reduce the access time. Although the advantage can be obtained at the first torsional resonance frequency, no advantage can be obtained at a higher-order torsional resonance frequency, whereby unstable motion is caused. Moreover, the need for various adjustments makes it difficult to reduce the number of man-hours required in production. For example, the variations in the distance between the support arm and the disk in production require the adjustment for each head support device, and in addition to the adjustment to the curved shape of the plate spring of the support arm for the purpose of suppressing the first torsional mode of the support arm, an adjustment is required, for stable performance, to suppress a characteristic change resulting from a change in setting height (Z-height) of the support arm. To solve these problems, a so-called balancing type head support device is proposed (refer to, for example, Japanese Patent Unexamined Publication No. 2002-260356).
Another proposal improves reliability by preventing a break in wiring. According to this proposal, the head signal wiring of a flexure is passed through an opening (through hole) of the support arm for placement without folding (refer to, for example, Japanese Patent Unexamined Publication No. 11-039629).
In the above-mentioned conventional head support devices, although providing the cutout hole or the thin plate structure reduces the rigidity and the spring constant of the plate spring, thus smoothing out the variations in the urging force, an ideal spring, for which stress on the spring that occurs in application of the load of the slider is reduced and pressing of the slider is increased, has not been designed.
Recently, the magnetic head is moved to the target track at increasingly high speed. Accordingly, the torsional vibration frequency of the torsional vibration mode becomes extremely higher, thus problematically causing the head to get off the target track.
With the balancing type head support device such as mentioned above, rigidity of the head signal wiring between the support arm and the base arm causes loss of a balance, thus adversely affecting impact resistance and stability of pressing force.
The proposal that the head signal wiring of the flexure is passed through the opening (through hole) of the support arm certainly allows the placement of the wiring without folding. However, in consideration of the work required for passage of the flexure through the hole, this proposal is hard to adopt in terms of mass production.
Since size reduction, especially thickness reduction, is demanded of the overall magnetic recording/reproducing apparatus, the head support device must be reduced in thickness.
Not only the magnetic recording/reproducing apparatus but also other disk drives, each having the floating head, such as the optical disk drive and the magneto-optical disk drive, have these problems.